1. Field of the Invention
This invention relates generally to methods and systems providing telephony communications through a packet switched wireless network. A particular aspect of the invention relates to methods of transferring call related control messages in a packet switched wireless network.
2. Description of the Related Art
In general, packet switched wireless networks provide communications for mobile terminals with no physical connection required for network access. The General Packet Radio Service (GPRS) in the Global System for Mobile Communications (GSM) and the Universal Mobile Terrestrial System (UMTS) have both been developed to provide wireless communications networks with a packet switched side as well as a circuit switched side.
The specifications for a UMTS network with further improvements have been released by the 3rd Generation Partnership Project (www.3gpp.org). Release 99 of the UMTS specifications provides that a network subscriber can have one or more packet data protocol (PDP) addresses. Each PDP address is described by one or more PDP contexts in the Mobile Station (MS), the Service GPRS Service Node (SGSN), and the Gateway GPRS Service Node (GGSN). A GGSN is a gateway to an external network. Each PDP context may have forwarding and mapping information for directing the transfer of data to and from its associated PDP address and a traffic flow template (TFT) for filtering the transferred data.
Each PDP context can be selectively and independently activated, modified and deactivated. The activation state of a PDP context indicates whether or not data transfer is enabled for a corresponding PDP address and TFT. If all PDP contexts associated with the same PDP address are inactive or deactivated, then all data transfer for that PDP address is disabled. All PDP contexts of a subscriber are associated with the same Mobility Management (MM) context for the International Mobile Subscriber Identity (IMSI) of that subscriber.
An example of the PDP context activation procedure in Release 99 of the UMTS specifications is shown in FIG. 2. As known from the specifications, the PDP context activation procedure is slightly different depending on whether it is the first PDP context activation procedure for a particular PDP address or a subsequent PDP context activation procedure (called “secondary” PDP contexts).
The activate PDP context request message sent in step 1 of FIG. 2 includes a number of parameters. The parameters include a PDP address and an Access Point Name (APN). The PDP address is used to indicate whether a static PDP or dynamic PDP address is required. The APN is a logical name referring to the Gateway GPSR Support Node (GGSN) to be used. In step 3, the SGSN sends a Radio Access Bearer (RAB) setup message to the UMTS Terrestrial Radio Access Network (UTRAN). In step 4, the SGSN sends a Create PDP Context Request message to the affected GGSN. The GGSN decides whether to accept or reject the request, If it accepts the request, it modifies its PDP context table and returns a Create PDP Context Response message. The SGSN then sends an Activate PDP Context Accept message to the User Equipment (UE) in step 5.
Despite the detailed specifications provided for packet routing and PDP context in Release 99 of UMTS, it does not provide for certain telephone calls which may need to be handled in a particular manner. For example, emergency 911 calls are to be routed to a public safety answering point (PSAP) without cost to the calling party even if the calling party is roaming beyond their home area. Because of their packet oriented nature, UMTS and other recently developed packet switched wireless communications networks have problems identifying such types of calls and treating them appropriately while simultaneously guarding against abuse or fraud.